[ALPS-users] diagonal correlations

[Michele Dolfi]

MEASURE_AVERAGE is compute the average among all sites, i.e. a scalar value.
MEASURE_LOCAL returns a list of measurements on all sites.

Best,
Michele

--
ETH Zurich
Dr. Michele Dolfi
Institute for Theoretical Physics
HIT G 32.4
Wolfgang-Pauli-Str. 27
8093 Zurich
Switzerland

dolfim at phys.ethz.ch
www.itp.phys.ethz.ch

+41 44 633 78 56 phone
+41 44 633 11 15 fax 

> On 6 Feb 2017, at 08:50, Robertson Esperanza <robbie.esperanza at gmail.com> wrote:
> 
> Oh, I forgot to mention that I'm using mps_optim application. How does the result of MEASURE_AVERAGE differ from MEASURE_LOCAL, if let's say I use "n" for these parameters? Thanks
> 
> On Mon, Feb 6, 2017 at 3:08 PM, Michele Dolfi <dolfim at phys.ethz.ch <mailto:dolfim at phys.ethz.ch>> wrote:
> Hello,
> 
> Could you please be a bit more specific about the application you are running?
> 
> You are right about the local measurement, but you need MEASURE_LOCAL, since you want to value at each site. Since the n_i^2 operator is not yet defined in the model library, you need to add it yourself. Basically I would do as follow:
> 1. Copy the file models.xml from ALPS_ROOT/lib/xml/models.xml, where ALPS_ROOT is the root location of your alps installation.
> 
> 2. Add this definition to your local copy, it defines the n^2 operator
> <SITEOPERATOR name=“n_squared" site="x">
>   n(x)*n(x)
> </SITEOPERATOR>
> 
> 3. In your input parameters you have now to link to your new model file.
> MODEL_LIBRARY=“path/to/models.xml”
> 
> 4. And add your measurement
> MEASURE_LOCAL[Density^2] = “ n_squared"
> 
> 
> Hope this helps.
> 
> Best,
> Michele
> 
> --
> ETH Zurich
> Dr. Michele Dolfi
> Institute for Theoretical Physics
> HIT G 32.4
> Wolfgang-Pauli-Str. 27
> 8093 Zurich
> Switzerland
> 
> dolfim at phys.ethz.ch <mailto:dolfim at phys.ethz.ch>
> www.itp.phys.ethz.ch <http://www.itp.phys.ethz.ch/>
> 
> +41 44 633 78 56 <tel:+41%2044%20633%2078%2056> phone
> +41 44 633 11 15 <tel:+41%2044%20633%2011%2015> fax 
> 
>> On 6 Feb 2017, at 07:26, Robertson Esperanza <robbie.esperanza at gmail.com <mailto:robbie.esperanza at gmail.com>> wrote:
>> 
>> Hello,
>> 
>> I only started studying many-body physics, so there might be gaps in my knowledge. When using the MEASURE_CORRELATION, why does the measurement goes for only site i<j, is it because there will be "blowing up"? 
>> 
>> Alternatively, to measure for i=j, i think I could use MEASURE_AVERAGE, of let's say (n_i)^2 where n - n_up + n_down. How could I define such measurement, where you use an operator successively? Thank you for replying
>> 
>> Robertson Esperanza
>> 
>> 
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